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There is (offshore wind powered) light at the end of the tunnel!

by Jerome a Paris Mon Jan 25th, 2010 at 06:35:07 AM EST

bankers walking inside a foundation for the Belwind offshore windfarm,
Zeebrugge, Belgium, 22 January 2010

I went on a visit of the port site in Zeebrugge where the foundations for the Belwind offshore wind farm (the financing of which I worked on) have been stored before their installation and wanted to give you a glimpse of the kind of logistics that entails and what kind of problems can happen (and how they are solved).

Follow me below for a tour of a small bit of Europe's fastest growing heavy industry.

Part of the windpower series

As a quick reminder, there are 3 main types of foundations for offshore turbines: monopiles, gravity-based, and jackets/tripods.

Source: www.offshorewind.net

Here are gravity-based foundations and tripods:
See more here: The unexpected weight of hope

Monopiles have typically been used for smaller turbines and lowers depths, as their size (diameter and thickness) needs to increase with the load to be carried and their cost can become an issue. The price of steel will heavily influence the choice between the technologies when several are possible. In this case, with 3MW turbines in 20m depth, monopiles were the most logical choice.

Foundations include two main parts, the foundation itself (the part that's driven into the subsoil) and the transition piece (the part that's affixed on top of the foundation and carries the turbine tower).

two foundations on the ground
with several transition pieces in the background

The transition piece usually includes the boat landing, access platform and j-tubes (the steel tube that protects the electrical cable going to other turbines and/or the transformer station, it is curved near the ground to allow the cable to go from its underground trench to the turbine, thus its name).

On the left, you can see the bottom part of the j-tube,
while the right picture has the more complex set of j-tubes for the transformer station,
which has several cables going to several "strings" of turbines.
Note the anti-corrosion protection on the j-tubes.

It also plays a vital role in that it corrects any flaws in the verticality of the foundation: turbines require the towers to be within one half degree of perfect verticality in order not to have to bear inappropriate loads, and it is not so easy to hammer 50m long steel columns in the sea ground to such precision; the transition piece is designed to be adjusted to provide the perfect position required for the turbine over the water.

Another aspect which requires a lot of precision is the roundness of the foundation and the transition piece. The two of them must fit together (more on this in a second), and the transition piece needs to be in the exact size for the first part of the turbine tower to be bolted on top of it - tolerances are below a centimeter (the bolts are big ones - a couple centimeters thick, but they need to fit in over the whole diameter of the two parts...) for equipment measured in tens of meters.

The foundations here have a smaller diameter in their top part, in order for the transition piece to be lowered on top of them and around them. The two parts are then grouted together (a special concrete is injected between the two pieces, this is done on site, naturally, and under water).

the narrower top part of the foundation is quite visible on this picture.
Note the steel tubes alongside the transition piece in the foreground;
the j-tubes will be attached to these alongside the foundation part under water.

Some offshore windfarms use a different connection between foundation and transition piece, with the trnasition piece snuggling inside the foundation. One European windfarm has quality issues on the grouting in that configuration, and there are worries that the turbines could slip lower into the foundations (which is not that important) and lose their horizontality (which is a big problem...). with the design here this is less of an issue as the wider diameter below acts as a stop should the grouting fail.

"Ovality" is also an issue for foundations as the transition pieces need to fit on top of them, and it needs to be checked carefully.

oops - ovality

As you can see, the above foundation has a serious problem: it's really not round. In that case, it is not a manufacturing problem: that foundation sank during the transport to site and hit the seabed... The project company, together with the insurance companies, is investigating the best way to deal with this problem: replace it completely, try to improve its roundness by squeezing it back into shape (the giant steel "pinch" for that was being prepared on site when we visited) or, quite possibly, use it as it is (by luck, it is the bottom part which was damaged, ie the part that goes in the sand, so ovality is less of an issue there as long as the vertical penetration in the soil can still be controlled).

The reason the foundation sank is that it was transported to site by floating it - plugs were installed on each end and the foundation could simply be pulled on the water.

the two plugs used to float a foundation,
installed on the next one about to go to site.
One of these is filled with foam, as it needs to be taken off underwater,
when the foundation has been raised vertically,
and the foam makes it float back to the surface to be recovered.

But the design of a plug was found (after a number of trips) to be slightly faulty and water seeped in, leading to the incident. The foundation was recovered, and the design flaw was identified and has now been corrected. Transport of the foundations to the site was of course interrupted during the investigation, but by luck the weather was poor at that time so no work could have been done in that period... The pictures above show the new improved plug system, which includes a more comprehensive set of sensors to warn of any risk of infiltrations...

This is a fairly typical offshore construction incident, in that it was unexpected, hitting a system that had worked fine previously and had not altogether minor consequences. It was a technical problem, to which a technical solution could be found reasonably easily. It had an impact on the schedule, which could be absorbed by the buffers put in place (and indeed in this case did not require more buffers than were required because of bad weather anyway). In terms of financial impact for the project, it will be fairly minor as this can be largely minimized by repairs or covered by insurance. It goes to confirm that the goal cannot be to expect a flawless project, but to have teams which are able to deal with problems as they appear, because they _inevitably_ will appear at some point, and to have a budget and scheduled which include contingencies and are able to withstand such incidents. Resiliency is the key word here...

this is the special piece of equipment used to "grab" foundations
and bring them from their horizontal transport position to the vertical on site.
It was temporarily on site for some repairs/maintenance.

The project is expected to finish installing the foundations and transition pieces in the short future, and move on to the installation of the turbines. These are going to be soon delivered to a harbour site nearby (so, no pictures this time), with completion in the course of this year. The turbines will be erected on their towers on the site inland, and transported as a whole to the site - the erection is expected to attract quite a bit of attention in the area as it will be highly visible.

It's a busy harbor. During our site visit, we got to see the largest LNG tanker, and the largest container ship:

In the long run, we're all dead. John Maynard Keynes

by Jerome a Paris (etg@eurotrib.com) on Sun Jan 24th, 2010 at 02:41:30 PM EST
on dK: http://www.dailykos.com/storyonly/2010/1/24/829699/-There-is-(offshore-wind-powered)-light-at-the-end-of-the-tunnel!

on TOD: http://europe.theoildrum.com/node/6154

In the long run, we're all dead. John Maynard Keynes

by Jerome a Paris (etg@eurotrib.com) on Sun Jan 24th, 2010 at 04:07:55 PM EST
[ Parent ]
how is corrosion controlled with all that steel in seawater?
by njh on Sun Jan 24th, 2010 at 04:28:18 PM EST
It appears they are using a more reactive metal, such as zinc, electrically attached to the pipe. It would "soak up" excess electrons generated by stray currents in the structure. Or is that just my hyperactive imagination, Jerome?

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Sun Jan 24th, 2010 at 05:13:26 PM EST
[ Parent ]
no, that's exactly it.

In the long run, we're all dead. John Maynard Keynes
by Jerome a Paris (etg@eurotrib.com) on Sun Jan 24th, 2010 at 05:18:04 PM EST
[ Parent ]
I'm back for a few days, and cannot resist a temptation such as a scientific question/answer.

For more details, the corrosion process in work here is galvanic corrosion. All metals can be put on a scale of corrosion-readiness, with gold on top. When two metallic parts are electrically connected (as when both of them are inmersed in water), one of them will concentrate all the corrosion, while the other will remain protected.

The corrosion process itself consists in electrons flowing from the corroded part to the protected part, leaving ionized atoms getting away from the metal.

In marine applications, Zinc is used as easy-to-corrode metal, because it protects all metals usually employed in metallic contructions (steel alloys included).

In the image below, Copper is more corrosion-resistant than steel, so steel is corroded. But Steel is mechanically more resistant than copper, so the structure may weaken. The solution is to use sacrificail Zinc connection between both metals. It will protect both pipes, but will require periodic maintenance (easy: to replace the sacrificial Zinc part).
schematical representation of galvanic corrosion process

an anodic Zinc sacrificial part

by Xavier in Paris on Mon Jan 25th, 2010 at 03:51:39 AM EST
[ Parent ]
Oh yes, we did sacrificial anodes and galvanic protection (where you provide the electrons directly from a wind turbine, and make the anode either something that doesn't corrode (perhaps carbon?) or something you don't care about (old cars and tractors, apparently!)) at school, I was just wondering whether they even attempted to paint them, or use special steel or whatever.

So my question for you is: why do zinc coated things last a lot longer than steel?  If zinc is more reactive why doesn't it all just disappear quickly and revert to iron?

by njh on Mon Jan 25th, 2010 at 06:01:50 AM EST
[ Parent ]
The foundation pipes will be rammed into the ground, I don't think any coating will survive this procedure. Special (sea water resistant) steel would be too expensive, given the large quantities necessary.
Zinc coating is a bit different: The corrosion protection results from the coating of the entire surface. Within air the zinc forms a dense coating of zinc carbonate that protects the zinc from further corrosion.
Of course if the zinc layer is destroyed at some place the electrochemical process begins and its speed will depend on the area affected and the amount of humidity and ions present.
But even without holes in the coating the zinc layer degrades at free air, I believe it is roughly about 1µm/a.


by josch222 on Mon Jan 25th, 2010 at 06:55:40 AM EST
[ Parent ]
So zinc is both a cathodic protector and a 'paint'.  That's very clever.  Does water attack the zinc carbonate, or is it also ok in fresh water?  sea water?

I guess zincalum is better because aluminium oxide is so hard and inert.

Thanks for the chemistry lesson!

by njh on Mon Jan 25th, 2010 at 05:10:10 PM EST
[ Parent ]
Yes, as long as it is a complete coating it works as a kind of paint, if it is pierced it begins to work as a sacrificial anode, at least at this area.
As far as I know zinc carbonate is soluble in fresh water only in very small amounts, but I don't know about sea water. I think this depends on the kind and amount of other ions (esp. chlorine) present, and as one can deduce from the fact that sacrificial anodes work, it will be destroyed when the zinc is connected electrically to a chemical nobler metal.
Don't know about Zincalum.
by josch222 on Tue Jan 26th, 2010 at 04:37:44 AM EST
[ Parent ]
Maybe Cl- ions will have the same effect as for alumina, ie, hole piercing!
by Xavier in Paris on Tue Feb 9th, 2010 at 12:56:42 PM EST
[ Parent ]
same as ship hulls - with chunks of lesser metals covering the surface of the steel (Im hopeless, I never know if it's anodic or cathodic protection, maybe the chemists on board can help).

In the long run, we're all dead. John Maynard Keynes
by Jerome a Paris (etg@eurotrib.com) on Sun Jan 24th, 2010 at 05:17:30 PM EST
[ Parent ]
It is called "sacrificial anode":
<a href="http://en.wikipedia.org/wiki/Sacrificial_anode">http://en.wikipedia.org/wiki/Sacrificial_anode</a>
It uses the destructive effect of electrochemical corrosion to protect the steel.

The german article
<a href="http://de.wikipedia.org/wiki/Opferanode">http://de.wikipedia.org/wiki/Opferanode</a>
mentions a way to use cheap material if an electrical current is forced between the steel and the sacrified material. Zinc is more expensive than steel and electricity should not be a problem, so this variant may be used in offshore windpower. But I don't know for shure.

The picture with the tripod looks like the turbine at Hooksiel (a single near-shore installation for testing and exercising). In 2008 I was on vacation there and saw some preparations for the erection going on.
<a href="http://www.bard-offshore.de/en/projects/nearshore/hooksiel">http://www.bard-offshore.de/en/projects/nearshore/hooksiel</a>


by josch222 on Mon Jan 25th, 2010 at 03:53:16 AM EST
[ Parent ]
yes, it is the first prototype installed in water of the BARD 5MW turbine. I put up more pictures of their factories here: http://www.eurotrib.com/story/2009/3/12/114958/542

In the long run, we're all dead. John Maynard Keynes
by Jerome a Paris (etg@eurotrib.com) on Tue Jan 26th, 2010 at 03:33:06 PM EST
[ Parent ]
Right on both counts: it's cathodic protection through the use of a sacrificial anode.

One of the most common installations for my photovoltaic systems, back when I was a PV designer in the 1990s, was cathodic protection of oil pipelines.  (others included powering hazard warning lights on oil rigs, and microwave telecom relays for PDO Oman). Renewables helping out the fossil fuel industry.  Strange world, huh?

by LondonAnalytics (Andrew Smith) on Mon Jan 25th, 2010 at 09:34:49 AM EST
[ Parent ]
I don't think it is strange. I believe the fossil fuel industry is not so much ideological about renewables.
It is simply about maximizing profit. They really like it when (and are pushing for) their propaganda departments and politicians take an ideological approach to prolong the use of their existing infrastructure and monopolies in this field.
Especially as the stuff gets more and more expensive over time they try to squeeze as much as possible out of it. But in fact they are already heavily investing (and profiting) from renewables. They simply don't talk so much about it but of course they want to control the inevitable transition.
From my experience they use every technology available and have no reservation with green technology. I'm developing customer specific electronics and software for Li-battery management systems which are used in all kind of stuff that moves around: cars, buses, bikes, planes, inspection robots and AUVs. Although this is not exclusively "green" technology, it is somewhat related because of the hype of electric and hybrid cars and other projects (like Solar Impulse etc.). But of course the raw material industry uses the advantages of Li-Batteries for offshore prospection, pipeline inspection and the like.
I think they will use wind and solar energy to get the last drops of oil (and other resources) in a few decades, not for burning it up in cars or power plants but maybe for expensive drugs or otherwise difficult to produce plastics or other needed products.

I would use the old offshore oil and gas platforms to set up high voltage dc converters and the pipelines as protection pipes (or as the ground wire too) for the cables to the shore. Surrounding the platforms big offshore wind farms could be built then.
I'm pretty shure there are studies about that in the drawers of the fossil industry already.


by josch222 on Tue Jan 26th, 2010 at 06:14:42 AM EST
[ Parent ]
They really like it when (and are pushing for) their propaganda departments and politicians take an ideological approach to prolong the use of their existing infrastructure and monopolies in this field.

That's the key: they hate losing market share. However, the presently most widespread renewables -- on-shore wind, rooftop solar --, especially when paired with a feed-in law, are structurally predisposed to bring in many new small owners and thus break monopolies. The energy giants will (do) like off-shore wind much more (not to mention centralised solar power, hence the support for the IMO pie-in-the-sky Desertec). But, even when existing energy giants build renewables, they will be less enthusiastic about an accelerated replacement of their existing plants, though.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Wed Jan 27th, 2010 at 10:03:44 AM EST
[ Parent ]
Due to the overwhelming respooonse of the last Contest (one of J's diaries, zero) it's time to play again.

What offshore foundation technology has a chance of competing against the three current ones mentioned in this diary?  Clue:  they've already been used in near shore applications, but can be modified for deeper waters... and may be cheaper?  Not counting floating foundations.

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin

by Crazy Horse on Tue Jan 26th, 2010 at 04:28:05 PM EST
Artificial reefs?
by njh on Tue Jan 26th, 2010 at 05:28:42 PM EST
[ Parent ]

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Jan 27th, 2010 at 10:04:52 AM EST
[ Parent ]
Someone's getting warm here.

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin
by Crazy Horse on Wed Jan 27th, 2010 at 10:38:37 AM EST
[ Parent ]
OK I looked up how the suction method foundation is called properly: bucket, then?

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Jan 27th, 2010 at 10:49:38 AM EST
[ Parent ]
Suction Buckets!

Here's a prototype from 2003 for Enercon's then largest 4.5 MW turbine.

The British Study version

A vacuum is created within the bucket, which sinks itself into the seabed without hammering.  it's been used in offshore oil and gas, and there are several different types under study for varying offshore depths and conditions.  They have won the whale and dolphin "seal" of approval (though have not been tested enough yet for wind use).

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin

by Crazy Horse on Wed Jan 27th, 2010 at 11:17:08 AM EST
[ Parent ]
Prize portion of a rare Caol Ila to be delivered at a meetup to be discussed.  Congrat's DoDo.  

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin
by Crazy Horse on Wed Jan 27th, 2010 at 11:19:02 AM EST
[ Parent ]
BARD's tripiles?

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Jan 27th, 2010 at 10:25:19 AM EST
[ Parent ]
Basically a combination of two of the above.

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin
by Crazy Horse on Wed Jan 27th, 2010 at 10:39:12 AM EST
[ Parent ]
After Jérôme explained it for a monopile, the question arises: how do they regulate vertical alignment on a tripile?

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Jan 27th, 2010 at 10:51:55 AM EST
[ Parent ]
Currently same method although more measurement and correction intensive.

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin
by Crazy Horse on Wed Jan 27th, 2010 at 11:25:52 AM EST
[ Parent ]
Jérôme didn't state explicitely, but I took it that the transition piece can be rotated. However, to adjust a level surface on a tripole, I imagine height difference is needed.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Jan 27th, 2010 at 04:55:07 PM EST
[ Parent ]
Wait, maybe I miss the obvious solution. The platform on top of the tripole to which the tower will be fixed can be adjusted, right?

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Jan 27th, 2010 at 04:56:22 PM EST
[ Parent ]

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